Sytem recently power flushed,now new pump sucking in air-please help

[PSH]

Hi all,I am new to this forum. Just to give you a quick low down on what has happened so far. My Mother had a guy round to remove sludge in the central heating pipes which had practically stopped any water flow round the system ,and all but three of her rads remained cold. He refused to power flush her system because he said her system is micro-bore and would not stand the force ,so he dosed her system with chemicals and left her pump running for 3 days and came back expecting all the sludge to have gone.(I personally could not see how this would work as his chemicals would not be able to flow around her system ,so would not reach the blockages to break down the sludge, am i right ?) Any way ,he came back and there was no flow at all and all rads were stone cold. He turned the pump around several times to reverse flow the water to try and force sludge out,but this failed. He said that she needed all her pipes replacing with 15mm ones as flushing was not an option.

So I went through Age UK and this time got a "trusted" flushing firm round who said all it needed was to power flush her system and it was safe to do so. This second engineer successfully forced all the sluge out and got all her rads hot within 4 hours . He renewed her old pump as it had totally siezed up due to it running dry for too long caused by the sludge not allowing any water through it. This second enginner was un sure as to whether the first guy had put back the pump the right way round,but all seemed fine when he left ,and all rads were piping hot ,but after an hour ,all the rads went cold,even with the pump and boiler still running. I rang the guy up ,and he got me to bleed the new pump,which seemed to get all rads hot again. but they all went cold again after another hour,so he said he will come back to turn the pump around the other way,to see if that cures the problem.He also suspected air was being sucked in from the open vent,and suggested it might need an auto-bleed valve fitting to open vent,(what do you think of his suggestion guys)

My questiosn to you guys are ,has this new pump got a self venting valve ,as he told me to undo the black nut on top of unit and press it in ,which did release air.The pump is fitted on the return run.When i released the air form the pump a load of water shot out of the open vent and into the header tank,and continued to do this for a few minutes after system was running again.

Is the new pump sucking in air ,causing the rads to run cold after a while.
Please Help!

 

[PSH]

Hi,just to update you all, my Mums radiators are still running nice and hot (touch wood),with just the odd bit of bleeding required.The guy who did the power flushing asked me to turn the pump speed setting down to the mid way postion ,in case the pump is running too fast and is aerating the water, producing air bubbles.

I have fitted propper pipe insulation to all exposed pipe work in attic and fitted 2 new jackets to the storage tank. I am checking the magna flush filter regualary and have noticed that with each clean ,it is collecting less black sludge,which must be a sign that the water in the system is getting cleaner.

The guy who did the power flushing has agreed to come back and replace the boiler stat.

I have noticed that the ball valve in the heating header tank has a small leak,one drip every 15 seconds,which is being handled ok by the over flow pipe. I have replaced the small round black washers before in these valves ,but wanted to ask you guys if you think i should renew the whole assembly or just renew the washer ?